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Do the payload size check after the TXT and base32 checks.

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That way we can respond with NXDOMAIN rather than FORMERR to more of the
random queries that arrive.
This commit is contained in:
David Fifield
2020-04-19 00:59:04 -06:00
parent 04e1295e52
commit 59f03791df
1 changed files with 11 additions and 12 deletions
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dnstt-server/main.go
+11 -12
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@@ -283,18 +283,6 @@ func responseFor(query *dns.Message, domain dns.Name) (*dns.Message, turbotunnel
resp.Flags |= 0x0400 // AA = 1
}
// We require clients to support EDNS(0) with a minimum payload size;
// otherwise we would have to set a small KCP MTU (only around 200
// bytes). https://tools.ietf.org/html/rfc6891#section-7 "If there is a
// problem with processing the OPT record itself, such as an option
// value that is badly formatted or that includes out-of-range values, a
// FORMERR MUST be returned."
if payloadSize < maxUDPPayload {
resp.Flags |= dns.RcodeFormatError
log.Printf("FORMERR: EDNS payload size %d is too small (minimum %d)", payloadSize, maxUDPPayload)
return resp, clientID, nil
}
if resp.Flags&0x0400 == 0 { // AA
// Not a name we are authoritative for.
resp.Flags |= dns.RcodeNameError
@@ -331,6 +319,17 @@ func responseFor(query *dns.Message, domain dns.Name) (*dns.Message, turbotunnel
return resp, clientID, nil
}
// We require clients to support EDNS(0) with a minimum payload size;
// otherwise we would have to set a small KCP MTU (only around 200
// bytes). https://tools.ietf.org/html/rfc6891#section-7 "If there is a
// problem with processing the OPT record itself, such as an option
// value that is badly formatted or that includes out-of-range values, a
// FORMERR MUST be returned."
if payloadSize < maxUDPPayload {
resp.Flags |= dns.RcodeFormatError
return resp, clientID, nil
}
return resp, clientID, payload[len(clientID):]
}